It has long been the dream of automobile body shop operators to have a dent removal tool which is inexpensive, easy to operate, and capable of removing dents with minimal damage to the finished, external surfaces of the body. Optimally, the tool would permit dent removal without the necessity for subsequent sanding, grinding, or refinishing operations.
The commercial aircraft industry has had the same interests. The skin of airplanes frequently becomes dented and requires repair, much like that of an automobile body. Unlike most automobiles, however, the skin of airplanes is conventionally made of aluminum. Automobiles, of course, normally have sheet steel bodies.
There have been numerous tools developed for dent removal from both automobile and airplane bodies. These include electromagnetic tools and pure mechanical tools. A brief discussion of a number of U.S. patents disclosing such tools is in order to more completely understand the prior art background against which the present invention was made.
The Reed U.S. Pat. No. 2,510,253 shows a mechanism for removing dents from automobile bodies or other articles constructed of magnetic sheet material. An electromagnetic apparatus, properly positioned, removes a dent from a sheet metal object upon energization of the electromagnetic means. A high degree of magnetization is effected to draw a workpiece flat against the face of a matrix formed in the shape of the desired surface.
The Sanchez U.S. Pat. No. 2,605,658 employs a sliding hammer which is adapted to produce a sharp shock or hammer blow to straighten a dent. An electromagnet secures the head of the tool to the base of a dent in an automobile door panel, for example. Actuation of a hammer device on the tool moving outwardly of the tool, is effective to pull the dent out of the panel, assisted by the electromagnetic force attraction of the head to the door panel.
The Crowder U.S. Pat. No. 2,696,240 uses magnetic metal elements which are placed on opposite sides of a dented metal skin in an aircraft or boat, for example. At least the outer member is an electromagnet, which is mounted on a tripod through screw adjustment means. After the magnet current is turned on, the screw is revolved and the member opposite the panel, which acts as an armature, slowly pushes out the dent as it follows the electromagnet on the screw.
The Furth U.S. Pat. No. 3,196,649 makes use of what it calls a "magnetic tension technique" of metal forming. In the first step, a magnetic field is generated in a primary coil that is held near the surface of the work. The device magnetically forms the metal workpiece by exerting magnetic pressure which pulls the workpiece toward the electrical conductor generating the magnetic field.
The Hanson et al. U.S. Pat. No. 3,998,081, the Hanson et al. U.S. Pat. No. 4,116,031, and the Hanson et al. U.S. Pat. No. 4,135,379, all show electromagnetic dent pullers developed primarily for the aircraft industry. These patents are all assigned to the Boeing Company, Seattle, Wash. Each uses powerful electromagnets using pulse field technology to remove dents.
These tools have had, for one reason or another, limited commercial success. This is particularly true in the automobile repair business, where no practical dent pulling tool which is effective but not prohibitively expensive has emerged.